1. Field of the Invention
The present invention relates to a communication system, a communication controller and a communication control method associated with a plurality of communication modes, and more particularly to a communication system, a communication controller and a communication control method for portable telephones associated with a voice service mode and a television telephone mode.
2. Description of the Prior Art
A communication system associated with a plurality of communication modes is well known. For example, a portable telephone communication system of the third generation is associated with a voice service mode using a voice channel, a television telephone mode using the voice channel and a video channel, and a data communication mode using a data channel, and further a television conference mode using the voice channel and the video channel to enable three or more terminals to be connected at the same time. In the future, it is expected that the communication modes are diversified because the kind of channel, the number of use channels, and connection forms are increased.
By the way, if the communication modes are diversified, it is necessary to take into consideration a difference in the communication mode associated state between terminals. For example, the methods have been offered in which when a portable telephone terminal having a television telephone function calls a portable telephone terminal without television telephone function in the television telephone mode, a switching center automatically switches to the voice service mode, and the originating portable telephone set automatically recalls in the voice service mode upon a communication disconnect of the called portable telephone terminal.
However, with the above methods, since the called portable telephone terminal is once connected and the communication mode is switched in response thereto, there is a problem that a wasteful traffic occurs. Also, according to the above methods, even though both terminals can deal with the television telephone mode, when the originating portable telephone terminal calls in the voice service mode, the called portable telephone terminal is directly connected in the voice service mode, resulting in a problem that the opportunity of using the television telephone function is reduced.
Thus, a communication controller that optimizes the connection in accordance with connection destination information registered by the user of connection source has been offered (e.g., refer to Japanese Unexamined Patent Publication No. 2003-298744). If such communication controller is employed, there is less connection error between terminals caused by a difference in the communication mode, making it possible to suppress wasteful traffic.